1. Field of the Invention
The present invention relates to a battery voltage monitoring apparatus used to monitor battery voltage.
2. Description of the Related Art
There has been proposed in, for example, Japanese Unexamined Patent Publication No. 2007-244058 a capacity adjustment apparatus, which includes monitor integrated circuits (hereinafter referred to as monitor ICs) each of which monitors the state of cells connected in series. The “capacity” in this publication means a charge level or an SOC (state of charge). In this capacity adjustment apparatus, each monitor IC is responsible for the same number of cells.
If the capacity adjustment apparatus is designed to receive operation power from the cells, which are the objects to be monitored, a consumption current in each monitor IC can vary. Therefore, it has been proposed that the capacity adjustment apparatus should discharge the cells in accordance with the variation in the consumption currents between the different monitor ICs, for equalization of the capacity of the cells.
Although in the conventional prior art (the capacity adjustment apparatus) each of the monitor ICs is responsible for the same number of cells, the number of cells to be provided to each monitor IC is not always the same. Therefore, as the number of the cells connected to each of the monitor ICs differs, the consumption current flowing in each of the monitor ICs varies. This is because each monitor IC has a resistance load, and the higher the applied voltage is, the higher the current consumption is. As a result, if the monitor ICs with different current consumptions are used continuously, the voltages of the cells in each of the monitor ICs vary, and thus it is necessary to frequently equalize the voltages of the monitor ICs.
In order to properly equalize the voltages of the cells, it is necessary to perform the equalization operation while a vehicle is stopped. However, the equalization of the voltages of high capacity cells requires a considerable amount of time. If the equalization is required frequently, there may be insufficient time to properly perform the equalization operation for vehicles such as taxis, which run continuously.
The same problem may take place, not only when the capacity adjustment apparatus is mounted on a vehicle, but also when the capacity adjustment apparatus is used continuously in a factory, for example.